Hitherto, many metals such as tungsten and aluminum have been widely used as interconnecting materials in many electronic devices such as semiconductors. However, an aluminum interconnect (specific resistance: about 2.7 .mu..OMEGA..cm) tends to be hampered by the problem of electromigration, while tungsten has the problem of high resistivity (specific resistance: about 5.4 .mu..OMEGA..cm). Therefore, attempts have recently been made to use copper which is highly conductive (specific resistance: about 1.67 .mu..OMEGA..cm) and electromigration resistant, as an interconnecting material in advanced devices such as ultra-large semiconductor integrated circuits.
A metallic interconnect is typically formed by a chemical vapor deposition (CVD) method using a metallorganic precursor compound, and Cu films have previously been prepared using various organic copper precursors such as Cu(II)(hfac).sub.2, wherein hfac stands for hexafluoroacetyl-acetonate. However, a CVD process using such Cu(II) precursors requires a high deposition temperature and the resulting Cu film is often contaminated by various impurities.
Organic copper(I) precursor compounds usable in a low temperature, selective CVD process have been recently developed. For example, the use of organocuprous precursors such as (hfac)Cu(I) (vinyltrimethylsilane) and (hfac)Cu(I) (allyltrimethylsilane) in a low temperature CVD process to selectively deposit a Cu film on a conductive substrate surface has been disclosed by Norman et al. in U.S. Pat. No. 5,085,731. However, the CVD using the above Cu(I)-vinylsilane precursors provides copper films having poor step-coverage and hole-filling characteristics.
U.S. Pat. No. 5,098,516 teaches the use of Cu(I)-olefin precursors such as (hfac)Cu(I).COD (COD: cyclooctadiene) and (hfac)Cu(I).NBD (NBD: norbonadiene) in a low temperature CVD process. The above Cu(I)-olefin precursors are solids, and for their vaporization, they are sublimed at a temperature below their thermal decomposition temperatures, e.g., about 105.degree. C. for (hfac)Cu(I).COD. Thus, the CVD process; disclosed in U.S. Pat. No. 5,098,516 is hampered by the difficult problem of handling solid precursors in a mass production system. Moreover, the CVD of a copper film using, e.g., (hfac)Cu(I).COD requires a relatively high substrate temperature of above 150.degree. C. and the resulting copper film is often of poor quality.